This invention relates to a system comprising an apparatus and a method for use in drying technology. The invention will be described with reference to the introduction of moist material into the apparatus, the drying of the material, and the collection of the material from a drying chamber. In a typical application, the material entering the apparatus will be in the form of a pumpable solution or slurry, and the system will result in a dry powder exiting from the drying chamber.
The system of the invention more specifically comprises the use of pulse combustion for achieving the drying function. Pulse combustion drying generally relates to the provision of a pulse combustor and associated combustion chamber with fuel being introduced into the combustion chamber. The fuel is mixed with air in the combustion chamber, and this mixture is periodically self-ignited to create high frequency, high energy, sonic pulsations.
More specifically, a tail pipe is associated with the combustion chamber for achieving release of the hot gases from the combustion chamber on a periodic basis. In the operation of such a system, the momentum of the combustion products issuing from the combustion chamber as the result of ignition and explosion will create a reduced pressure in the combustion chamber to draw in a new air and fuel charge which is again self-ignited to achieve the next explosion. The result achieved with a pulse combustor of this type constitutes a pulsating flow of hot gases issuing from the tail pipe. As explained, for example, in Lockwood U.S. Pat. No. 4,708,159, the frequency of pulses may be 100 times per second or higher. It is also well established that the temperature of the products of combustion issuing from the tail pipe will be at least about 1800.degree. F. with temperatures exceeding 2300.degree. F. frequently resulting.
In a typical system, the pulsating flow of hot gases is brought into contact with material introduced to the system at the exit end of the tail pipe. This material, which may be in the form of a slurry, will be "atomized" by the hot gas pulses which results in rapid drying. Under these circumstances, material can be collected as a fine, dry powder.
Difficulties have been recognized with certain types of material when the material is exposed to the high temperatures which characterize pulse combustion drying. Certain materials, for example protein products, may be denatured if exposed to such high temperatures for even a very short amount of time. Other materials may be "scorched" or otherwise damaged due to such exposure.